This invention relates to a braking device for a vehicle. In particular, this invention relates to a technique of optimizing control of a brake device in a vehicle using a load as a braking force, the load occurs when an electrical motor driving the vehicle generates electricity during braking.
A vehicle is provided with an electrical motor for driving the vehicle which uses a battery as a power source, and is provided with a controller comprising a microcomputer for controlling the electrical motor, which controls the electrical motor so that a required drive torque is generated in response to an operational condition signal such as the stroke amount of an accelerator pedal, is known in the prior art.
In this type of vehicle, when the accelerator pedal is released, the load on the electrical motor which had been driving the drive system including the drive wheels is reversed. The electrical motor is driven by the drive system. At this time, regeneration braking control is performed to make effective use of the inertial energy of the vehicle. That is to say, generation of electricity is performed in the electrical motor by the driving force from the drive system. The generating load on the electrical motor at this time is used as a braking force and the generated electricity from the electrical motor is supplied to charge the battery. However when this type of vehicle is slowing down, the possibility exists of overcharging the battery as the braking force of the braking device and the amount of generated electricity from the electrical motor are not limited to an appropriate range for a required braking force determined in response to a brake pedal operational amount. On the other hand, Tokkai-Hei-8-308016 published by the Japanese Patent Office in 1996 discloses a control which is performed not with the regeneration amount of the electrical motor but in a generator driven by the engine in order to prevent over-supply of electricity during regenerative braking of the electrical motor in the electrical generator of a hybrid drive system.
The present invention is proposed to solve the above problem and has the object of maximizing the regenerative braking force of the electrical motor in a range of the electricity supply amount to the battery while satisfying the required braking force in response to the brake pedal operational amount. This is enabled by controlling the regenerative braking force of the electrical motor and the braking force of the braking device during braking of the vehicle.
The braking force calculation means calculates a driven-wheel braking force BFO in response to a braking operational amount of the driver, a driving-wheel braking force BRO and a driven-wheel minimum required braking force BFM. The required braking force calculation means calculates the required braking force BO=BFO+BROxe2x88x92BFM based on each braking force. The first regenerative braking calculation means calculates the regenerative braking force BM which can be generated by the electrical motor. The second regenerative braking force calculation means calculates the regenerative braking force BB of the power supply equivalent input to the battery. The regenerative braking force setting means compares the values BM and BB and sets BM as a regenerative braking force BM of the electrical motor when is BB greater than or equal to BM and sets BB as the regenerative braking force BM when is BB smaller than BM. Furthermore a regenerative braking control means is provided which compares the set regenerative braking force BM and the required braking force BO and controls the electrical motor and the braking mechanism. When BMis greater than or equal to BO, a required braking force BO is generated only by the electrical motor, while generating the driven-wheel minimum required braking force BFM. When BM is smaller than BO, a regenerative braking force BM is generated by the electrical motor while generating the driven-wheel minimum required braking force BFM and the remainder of the braking force is generated by the vehicle braking mechanism in the range of the driving-wheel braking force BRO and the driven-wheel braking force BFO.
When a braking operation is performed while the vehicle is slowing down, this invention allows the calculation of the driving-wheel braking force BRO, the driven-wheel braking force BFO and the driven-wheel minimum required braking force BFM in response to the braking operational amount. Thus it is possible to calculate a required braking force BO=BFO+BROxe2x88x92BFM. A regenerative braking force BM generated by the electrical motor and the regenerative braking force BB of the power supply equivalent input to the battery are calculated. The comparison of the values BB and BM allows a regenerative braking force BM of the electrical motor to be re-set as BM when BB is greater than or equal to BM or as BB when BB is smaller than BM. When BM is greater than or equal to BO, only the electrical motor generates the required braking force BO by control based on a comparison of the regenerated braking force BM and the required braking force BO. The driven-wheel minimum required braking force BFM is generated by the braking mechanism. When BM is smaller than BO, the driven-wheel minimum required braking force BFM is generated by the braking mechanism and the regenerative braking force BM is generated with the electrical motor.
The remainder is generated by the braking mechanism in the range of the driving-wheel braking force BRO and the driven-wheel braking force BFO. Thus it is possible to prevent over-supply of electricity to the battery while satisfying the braking force required by the brake operational amount. In this way, it is possible to optimize the generation of a regenerative braking force by the electrical motor in a permitted battery range. Furthermore since a braking force above the minimum required braking force acts on the driven wheel, it is possible to generate a required braking force only with the electrical motor and thus it is possible to maintain sufficient operational stability in the vehicle.
It is possible to apply various types of controllable braking mechanisms in a control device comprising a microcomputer or the like to the braking force as a vehicle braking mechanism. These types of braking mechanisms comprise a brake plunger, a pressure proportion control valve, and a pressure regulation means. The brake plunger operates a braking force on vehicle wheels based on the pressure from a pressure source for example. The pressure proportion control valve adds pressure in response to commands from a control means and/or a brake pedal operational amount of the driver. The pressure regulation means comprises a solenoid pilot operation section, a cut-off valve or the like which regulates the pressure supplied to the pressure proportion control valve in response to the brake pedal operational amount (the amount of brake pedal activation) based on commands from the regenerative braking control means. In this case, during regenerative braking, the regenerative braking control means suppresses the pressure in response to the brake pedal operational amount due to the pressure regulation means and the remainder of the regenerative braking force with respect to the required braking force is generated by the brake plunger by controlling the pressure proportion control valve.